1. Field of the Invention
The present invention relates to a semiconductor device and a method for fabricating a semiconductor device, and more particularly, to a semiconductor device having a multilevel interconnection layer and a method for fabricating such a semiconductor device.
2. Description of the Related Art
In a conventional method for fabricating such a semiconductor device, a stopper film such as an Si3N4 layer is used which is smaller in a polishing rate than an interlevel insulating film, as disclosed in JP-A-62-216344, for example. That is, an aluminum layer is formed through the stopper film on the interlevel insulating film in which an electrode window is formed. Thereafter, the aluminum layer is polished to be buried in the electrode window.
However, as more miniaturization and higher integration of a semiconductor element are advanced, it has become necessary to reduce the parasitic resistance and capacitance within an opening such as a contact hole or a via hole. To this end, there has been developed a method for filling into the opening a conductive plug which is made of a metal having a high melting point. More specifically, a high-melting-point metallic layer made of tungsten (W) or the like is formed on the entire surface of the semiconductor substrate including the inner wall of the opening through an underlying conductive layer made of Ti, TiN or the like. Thereafter, the high-melting-point metallic layer is subjected to the anisotropic etching process to be buried only into the opening, so that the conductive plug is formed. Then, an upper wiring layer made of aluminum alloy or the like is patterned so as to be connected with the conductive plug. However, such a method for forming the conductive plug has a disadvantage that, when the high-melting-point metallic layer is subjected to the anisotropic etching process, the metallic layer within the opening tends to be excessively etched, so that a recess takes place in the conductive plug. This involves such a problem that the recess causes the reduction of step coverage of the upper wiring layer, whereby the upper wiring layer tends to be more broken and a resultant semiconductor device is reduced in its reliability.
For the purpose of solving the problem, a method for fabricating a semiconductor device as disclosed in JP-A-7-240466, for example is proposed that a stopper film such as an Si3N4 film is formed on an interlevel insulating film and then a contact hole is formed in the stopper and interlevel insulating films. Thereafter, a tungsten plug film is covered on the stopper film including the contact hole. After that, the tungsten plug film is subjected to an etch-back process until the stopper film is exposed, so that the stopper film is removed. This prevents a recess from taking place in the tungsten plug. In such a method for fabricating a semiconductor device, however, the occurrence of the recess in the tungsten plug can be avoided, but the surface of the tungsten plug is extruded from the surface of the interlevel insulating film, so that it is impossible to perfectly prevent the upper wiring layer, which is formed on the interlevel insulating film and is connected to the tungsten plug, from being broken.
An object of the present invention is to provide a semiconductor device which can secure a sufficient reliability in the semiconductor device and can reduce the parasitic resistance and capacitance within an opening, and a method for fabricating such a semiconductor device.
In accordance with the first aspect of the present invention, the above object is attained by providing a semiconductor device which comprises: first and second conductive layers electrically connected to each other through a contact plug; a first insulating film formed on the first conductive layer and having a first opening reaching a surface of the first conductive layer; and a second insulating film formed on the first insulating film and having a second opening formed at the same position as the first opening, wherein the contact plug is filled within the first and second openings, has a surface substantially flush with a surface of the second insulating film, and contains a metal having a high melting point; and the second conductive layer is formed on the surface of the second insulating film and a surface of the contact plug.
In accordance with the second aspect of the present invention, there is provided a semiconductor device which comprises: first and second conductive layers electrically connected to each other through a contact plug; a first insulating film formed on the first conductive layer and having a first opening reaching a surface of the first conductive layer; a second insulating film formed on the first insulating film and having a second opening formed at the same position as the first opening; and an underlying conductive layer formed on bottom and side faces of the first opening and on a side face of the second opening, wherein the contact plug is filled within the first and second openings through the underlying conductive layer and has a surface substantially flush with a surface of the second insulating film; and the second conductive layer is formed on the surface of the second insulating film and a surface of the contact plug.
In accordance with the third aspect of the present invention, there is provided a method for fabricating a semiconductor device having first and second conductive layers electrically connected to each other through a contact plug, which comprises the steps of: forming a first insulating film on the first conductive layer; forming a second insulating film on the first insulating film; forming first and second openings, which expose a part of a surface of the first conductive layer, in the first and second insulating films, respectively: forming a high-melting-point metallic layer containing a metal having a high melting point on the second insulating film so as to bury the first and second openings; forming the contact plug by polishing the high-melting-point metallic layer using the second insulating film as a stopper film to leave the high-melting-point metallic layer within the first and second openings; and forming the second conductive layer on a surface of the second insulating film and a surface of the contact plug.
In accordance with the fourth aspect of the present invention, there is provided a method for fabricating a semiconductor device having first and second conductive layers electrically connected to each other through a contact plug, which comprises the steps of: forming a first insulating film on the first conductive layer; forming a second insulating film on the first insulating film; forming first and second openings, which expose a part of a surface of the first conductive layer, in the first and second insulating films, respectively; forming an underlying conductive layer on bottom and side faces of the first opening and on a side face of the second opening; forming a third conductive layer on the underlying conductive layer and the second insulating film so as to bury the first and second openings; forming the contact plug by polishing the third conductive layer using the second insulating film as a stopper film to leave the third conductive layer within the first and second openings; and forming the second conductive layer on a surface of the second insulating film and a surface of the contact plug.
In accordance with the fifth aspect of the present invention, there is provided a method for fabricating a semiconductor device having first and second conductive layers electrically connected to each other through a contact plug, which comprises the steps of: forming an insulating film on the first conductive layer; forming an opening, which exposes a part of a surface of the first conductive layer, in the insulating film; forming an underlying conductive layer on bottom and side faces of the opening and on the insulating film; forming a high-melting-point metallic layer containing a metal having a high melting point on the second insulating film so as to bury the opening; forming the contact plug by subjecting the high-melting-point metallic layer to an etch back process using the insulating film as a stopper film to leave the high-melting-point metallic layer within the opening; subjecting the insulating film to an etch back process by a preset amount in such a manner that a surface of the contact plug is substantially flush with a surface of the insulating film; and forming the second conductive layer on a surface of the insulating film and the surface of the contact plug.
In accordance with the sixth aspect of the present invention, there is provided a method for fabricating a semiconductor device having first and second conductive layers electrically connected to each other through a contact plug, which comprises the steps of: forming a first insulating film on the first conductive layer; forming a second insulating film on the first insulating film; forming a third insulating film having a preset thickness on the second insulating film; forming first to third openings, which expose a part of a surface of the first conductive layer, in the first to third insulating films, respectively; forming an underlying conductive layer on bottom and side faces of the first opening, on a side face of the second opening and on the third insulating film; forming a high-melting-point metallic layer containing a metal having a high melting point on the underlying conductive layer so as to bury the first to third openings; forming the contact plug by subjecting the high-melting-point metallic layer to an etch back process using the third insulating film as a stopper film to leave the high-melting-point metal within the first to third openings; removing the third insulating film by subjecting the third insulating film to an etch back process; and forming the second conductive layer on a surface of the second insulating film and a surfaces of the contact plug.
In accordance with the seventh aspect of the present invention, there is provided a semiconductor device which comprises first and second conductive layers electrically connected to each other through a contact hole; a first insulating film formed on the first conductive layer and having a first opening reaching a surface of the first conductive layer; a second insulating film formed on the first insulating film and having a second opening formed at the same position as the first opening, the second insulating film having an etching rate smaller than an etching rate of the first insulating film; a third insulating film formed on the second insulating film and having a groove, the groove being formed at a position of the first and second openings so as to expose a part of the second insulating film, the groove having a width larger than a diameter of the first or second opening; and an underlying conductive layer formed on the part of the exposed second insulating film and on side faces of the groove of the third insulating film, the underlying conductive layer containing a metal having a high melting point, wherein the contact hole includes the first and second openings, the second conductive layer fills the contact hole and also fills the groove of the third insulating film through the underlying conductive layer.